FreeBSD Man Pages

DEVSTAT(3) FreeBSD Library Functions Manual DEVSTAT(3)
NAMEdevstat, devstat_getnumdevs, devstat_getgeneration, devstat_getversion,
devstat_checkversion, devstat_getdevs, devstat_selectdevs,
devstat_buildmatch, devstat_compute_statistics, devstat_compute_etime --
device statistics utility library
LIBRARY
Device Statistics Library (libdevstat, -ldevstat)
SYNOPSIS#include <devstat.h>
intdevstat_getnumdevs(kvm_t*kd);
longdevstat_getgeneration(kvm_t*kd);
intdevstat_getversion(kvm_t*kd);
intdevstat_checkversion(kvm_t*kd);
intdevstat_getdevs(kvm_t*kd, structstatinfo*stats);
intdevstat_selectdevs(structdevice_selection**dev_select,
int*num_selected, int*num_selections, long*select_generation,
longcurrent_generation, structdevstat*devices, intnumdevs,
structdevstat_match*matches, intnum_matches,
char**dev_selections, intnum_dev_selections,
devstat_select_modeselect_mode, intmaxshowdevs, intperf_select);
intdevstat_buildmatch(char*match_str, structdevstat_match**matches,
int*num_matches);
intdevstat_compute_statistics(structdevstat*current,
structdevstat*previous, longdoubleetime, ...);
longdoubledevstat_compute_etime(structbintime*cur_time,
structbintime*prev_time);
DESCRIPTION
The devstat library is a library of helper functions for dealing with the
kernel devstat(9) interface, which is accessible to users via sysctl(3)
and kvm(3). All functions that take a kvm_t* as first argument can be
passed NULL instead of a kvm handle as this argument, which causes the
data to be read via sysctl(3). Otherwise, it is read via kvm(3) using
the supplied handle. The devstat_checkversion() function should be
called with each kvm handle that is going to be used (or with NULL if
sysctl(3) is going to be used).
The devstat_getnumdevs() function returns the number of devices regis-
tered with the devstat subsystem in the kernel.
The devstat_getgeneration() function returns the current generation of
the devstat list of devices in the kernel.
The devstat_getversion() function returns the current kernel devstat ver-
sion.
The devstat_checkversion() function checks the userland devstat version
against the kernel devstat version. If the two are identical, it returns
zero. Otherwise, it prints an appropriate error in devstat_errbuf and
returns -1.
The devstat_getdevs() function fetches the current list of devices and
statistics into the supplied statinfo structure. The statinfo structure
can be found in <devstat.h>:
struct statinfo {
long cp_time[CPUSTATES];
long tk_nin;
long tk_nout;
struct devinfo *dinfo;
long double snap_time;
};
The devstat_getdevs() function expects the statinfo structure to be allo-
cated, and it also expects the dinfo subelement to be allocated and
zeroed prior to the first invocation of devstat_getdevs(). The dinfo
subelement is used to store state between calls, and should not be modi-
fied after the first call to devstat_getdevs(). The dinfo subelement
contains the following elements:
struct devinfo {
struct devstat *devices;
uint8_t *mem_ptr;
long generation;
int numdevs;
};
The kern.devstat.allsysctl(8) variable contains an array of devstat
structures, but at the head of the array is the current devstat genera-
tion. The reason the generation is at the head of the buffer is so that
userland software accessing the devstat statistics information can atomi-
cally get both the statistics information and the corresponding genera-
tion number. If client software were forced to get the generation number
via a separate sysctl(8) variable (which is available for convenience),
the list of devices could change between the time the client gets the
generation and the time the client gets the device list.
The mem_ptr subelement of the devinfo structure is a pointer to memory
that is allocated, and resized if necessary, by devstat_getdevs(). The
devices subelement of the devinfo structure is basically a pointer to the
beginning of the array of devstat structures from the kern.devstat.allsysctl(8) variable (or the corresponding values read via kvm(3)). The
generation subelement of the devinfo structure contains the corresponding
generation number. The numdevs subelement of the devinfo structure con-
tains the current number of devices registered with the kernel devstat
subsystem.
The devstat_selectdevs() function selects devices to display based upon a
number of criteria:
specified devices
Specified devices are the first selection priority. These are
generally devices specified by name by the user e.g. da0, da1,
cd0.
match patterns
These are pattern matching expressions generated by
devstat_buildmatch() from user input.
performance
If performance mode is enabled, devices will be sorted based on
the bytes field in the device_selection structure passed in to
devstat_selectdevs(). The bytes value currently must be main-
tained by the user. In the future, this may be done for him in a
devstat library routine. If no devices have been selected by
name or by pattern, the performance tracking code will select
every device in the system, and sort them by performance. If
devices have been selected by name or pattern, the performance
tracking code will honor those selections and will only sort
among the selected devices.
order in the devstat list
If the selection mode is set to DS_SELECT_ADD, and if there are
still less than maxshowdevs devices selected,
devstat_selectdevs() will automatically select up to maxshowdevs
devices.
The devstat_selectdevs() function performs selections in four different
modes:
DS_SELECT_ADD In ``add'' mode, devstat_selectdevs() will select any
unselected devices specified by name or matching pat-
tern. It will also select more devices, in devstat
list order, until the number of selected devices is
equal to maxshowdevs or until all devices are
selected.
DS_SELECT_ONLY In ``only'' mode, devstat_selectdevs() will clear all
current selections, and will only select devices spec-
ified by name or by matching pattern.
DS_SELECT_REMOVE In ``remove'' mode, devstat_selectdevs() will remove
devices specified by name or by matching pattern. It
will not select any additional devices.
DS_SELECT_ADDONLY In ``add only'' mode, devstat_selectdevs() will select
any unselected devices specified by name or matching
pattern. In this respect it is identical to ``add''
mode. It will not, however, select any devices other
than those specified.
In all selection modes, devstat_selectdevs() will not select any more
than maxshowdevs devices. One exception to this is when you are in
``top'' mode and no devices have been selected. In this case,
devstat_selectdevs() will select every device in the system. Client pro-
grams must pay attention to selection order when deciding whether to pay
attention to a particular device. This may be the wrong behavior, and
probably requires additional thought.
The devstat_selectdevs() function handles allocation and resizing of the
dev_select structure passed in by the client. The devstat_selectdevs()
function uses the numdevs and current_generation fields to track the cur-
rent devstat generation and number of devices. If num_selections is not
the same as numdevs or if select_generation is not the same as
current_generation, devstat_selectdevs() will resize the selection list
as necessary, and re-initialize the selection array.
The devstat_buildmatch() function takes a comma separated match string
and compiles it into a devstat_match structure that is understood by
devstat_selectdevs(). Match strings have the following format:
device,type,if
The devstat_buildmatch() function takes care of allocating and reallocat-
ing the match list as necessary. Currently known match types include:
device type:
da Direct Access devices
sa Sequential Access devices
printer Printers
proc Processor devices
worm Write Once Read Multiple devices
cd CD devices
scanner Scanner devices
optical Optical Memory devices
changer Medium Changer devices
comm Communication devices
array Storage Array devices
enclosure Enclosure Services devices
floppy Floppy devices
interface:
IDE Integrated Drive Electronics devices
SCSI Small Computer System Interface devices
other Any other device interface
passthrough:
pass Passthrough devices
The devstat_compute_statistics() function provides complete statistics
calculation. There are four arguments for which values must be supplied:
current, previous, etime, and the terminating argument for the varargs
list, DSM_NONE. For most applications, the user will want to supply
valid devstat structures for both current and previous. In some
instances, for instance when calculating statistics since system boot,
the user may pass in a NULL pointer for the previous argument. In that
case, devstat_compute_statistics() will use the total stats in the
current structure to calculate statistics over etime. For each statis-
tics to be calculated, the user should supply the proper enumerated type
(listed below), and a variable of the indicated type. All statistics are
either integer values, for which a uint64_t is used, or floating point,
for which a longdouble is used. The statistics that may be calculated
are:
DSM_NONE type: N/A
This must be the last argument passed to
devstat_compute_statistics(). It is an
argument list terminator.
DSM_TOTAL_BYTES type: uint64_t*
The total number of bytes transferred
between the acquisition of previous and
current.
DSM_TOTAL_BYTES_READ
DSM_TOTAL_BYTES_WRITE
DSM_TOTAL_BYTES_FREE type: uint64_t*
The total number of bytes in transactions
of the specified type between the acqui-
sition of previous and current.
DSM_TOTAL_TRANSFERS type: uint64_t*
The total number of transfers between the
acquisition of previous and current.
DSM_TOTAL_TRANSFERS_OTHER
DSM_TOTAL_TRANSFERS_READ
DSM_TOTAL_TRANSFERS_WRITE
DSM_TOTAL_TRANSFERS_FREE type: uint64_t*
The total number of transactions of the
specified type between the acquisition of
previous and current.
DSM_TOTAL_DURATION type: longdouble*
The total duration of transactions, in
seconds, between the acquisition of
previous and current.
DSM_TOTAL_DURATION_OTHER
DSM_TOTAL_DURATION_READ
DSM_TOTAL_DURATION_WRITE
DSM_TOTAL_DURATION_FREE type: longdouble*
The total duration of transactions of the
specified type between the acquisition of
previous and current.
DSM_TOTAL_BUSY_TIME type: longdouble*
Total time the device had one or more
transactions outstanding between the
acquisition of previous and current.
DSM_TOTAL_BLOCKS type: uint64_t*
The total number of blocks transferred
between the acquisition of previous and
current. This number is in terms of the
blocksize reported by the device. If no
blocksize has been reported (i.e., the
block size is 0), a default blocksize of
512 bytes will be used in the calcula-
tion.
DSM_TOTAL_BLOCKS_READ
DSM_TOTAL_BLOCKS_WRITE
DSM_TOTAL_BLOCKS_FREE type: uint64_t*
The total number of blocks of the speci-
fied type between the acquisition of
previous and current. This number is in
terms of the blocksize reported by the
device. If no blocksize has been
reported (i.e., the block size is 0), a
default blocksize of 512 bytes will be
used in the calculation.
DSM_KB_PER_TRANSFER type: longdouble*
The average number of kilobytes per
transfer between the acquisition of
previous and current.
DSM_KB_PER_TRANSFER_READ
DSM_KB_PER_TRANSFER_WRITE
DSM_KB_PER_TRANSFER_FREE type: longdouble*
The average number of kilobytes in the
specified type transaction between the
acquisition of previous and current.
DSM_TRANSFERS_PER_SECOND type: longdouble*
The average number of transfers per sec-
ond between the acquisition of previous
and current.
DSM_TRANSFERS_PER_SECOND_OTHER
DSM_TRANSFERS_PER_SECOND_READ
DSM_TRANSFERS_PER_SECOND_WRITE
DSM_TRANSFERS_PER_SECOND_FREE type: longdouble*
The average number of transactions of the
specified type per second between the
acquisition of previous and current.
DSM_MB_PER_SECOND type: longdouble*
The average number of megabytes trans-
ferred per second between the acquisition
of previous and current.
DSM_MB_PER_SECOND_READ
DSM_MB_PER_SECOND_WRITE
DSM_MB_PER_SECOND_FREE type: longdouble*
The average number of megabytes per sec-
ond in the specified type of transaction
between the acquisition of previous and
current.
DSM_BLOCKS_PER_SECOND type: longdouble*
The average number of blocks transferred
per second between the acquisition of
previous and current. This number is in
terms of the blocksize reported by the
device. If no blocksize has been
reported (i.e., the block size is 0), a
default blocksize of 512 bytes will be
used in the calculation.
DSM_BLOCKS_PER_SECOND_READ
DSM_BLOCKS_PER_SECOND_WRITE
DSM_BLOCKS_PER_SECOND_FREE type: longdouble*
The average number of blocks per second
in the specified type of transaction
between the acquisition of previous and
current. This number is in terms of the
blocksize reported by the device. If no
blocksize has been reported (i.e., the
block size is 0), a default blocksize of
512 bytes will be used in the calcula-
tion.
DSM_MS_PER_TRANSACTION type: longdouble*
The average duration of transactions
between the acquisition of previous and
current.
DSM_MS_PER_TRANSACTION_OTHER
DSM_MS_PER_TRANSACTION_READ
DSM_MS_PER_TRANSACTION_WRITE
DSM_MS_PER_TRANSACTION_FREE type: longdouble*
The average duration of transactions of
the specified type between the acquisi-
tion of previous and current.
DSM_BUSY_PCT type: longdouble*
The percentage of time the device had one
or more transactions outstanding between
the acquisition of previous and current.
DSM_QUEUE_LENGTH type: uint64_t*
The number of not yet completed transac-
tions at the time when current was
acquired.
DSM_SKIP type: N/A
If you do not need a result from
devstat_compute_statistics(), just put
DSM_SKIP as first (type) parameter and
NULL as second parameter. This can be
useful in scenarios where the statistics
to be calculated are determined at run
time.
The devstat_compute_etime() function provides an easy way to find the
difference in seconds between two bintime structures. This is most com-
monly used in conjunction with the time recorded by the devstat_getdevs()
function (in structstatinfo) each time it fetches the current devstat
list.
RETURN VALUES
The devstat_getnumdevs(), devstat_getgeneration(), and
devstat_getversion() function return the indicated sysctl variable, or -1
if there is an error fetching the variable.
The devstat_checkversion() function returns 0 if the kernel and userland
devstat versions match. If they do not match, it returns -1.
The devstat_getdevs() and devstat_selectdevs() functions return -1 in
case of an error, 0 if there is no error, and 1 if the device list or
selected devices have changed. A return value of 1 from
devstat_getdevs() is usually a hint to re-run devstat_selectdevs()
because the device list has changed.
The devstat_buildmatch() function returns -1 for error, and 0 if there is
no error.
The devstat_compute_etime() function returns the computed elapsed time.
The devstat_compute_statistics() function returns -1 for error, and 0 for
success.
If an error is returned from one of the devstat library functions, the
reason for the error is generally printed in the global string
devstat_errbuf which is DEVSTAT_ERRBUF_SIZE characters long.
SEE ALSOsystat(1), kvm(3), sysctl(3), iostat(8), rpc.rstatd(8), sysctl(8),
vmstat(8), devstat(9)HISTORY
The devstat statistics system first appeared in FreeBSD 3.0. The new
interface (the functions prefixed with devstat_) first appeared in
FreeBSD 5.0.
AUTHORS
Kenneth Merry <ken@FreeBSD.org>
BUGS
There should probably be an interface to de-allocate memory allocated by
devstat_getdevs(), devstat_selectdevs(), and devstat_buildmatch().
The devstat_selectdevs() function should probably not select more than
maxshowdevs devices in ``top'' mode when no devices have been selected
previously.
There should probably be functions to perform the statistics buffer swap-
ping that goes on in most of the clients of this library.
The statinfo and devinfo structures should probably be cleaned up and
thought out a little more.
FreeBSD 10.2 December 15, 2012 FreeBSD 10.2